Tertiary methylamines are of great importance in the chemical industry for the production of process chemicals, catalysts and intermediates for higher value-added products.
It is known from EP 257 443 A1 (BASF AG) that trialkylamines (e.g. dimethylethylamine) can be prepared by reacting ammonia or primary amines with primary monohydric aliphatic alcohols having from 2 to 24 carbon atoms, preferably in the presence of hydrogen and in the presence of a hydrogenation/dehydrogenation catalyst. The reaction is carried out continuously in the liquid phase at a total pressure of from 50 to 300 bar and a molar excess of from 1 to 15 mol of the alcohol over the ammonia or the primary amine. In addition, the alkylation is carried out in the presence of alkali metal and/or alkaline earth metal oxides and/or hydroxides. The hydrogenation/dehydrogenation catalyst comprises essentially copper. In examples 1 and 3, ammonia is reacted with ethanol or n-butanol in the presence of sodium hydroxide to form triethylamine or tri-n-butylamine. The reaction is carried out at from 230 to 250° C., total pressures of 200 bar and hydrogen partial pressures of >150 bar or 120 bar. Apart from the tertiary amines as target products, only small amounts of secondary amines are formed.
In example 2, the primary amine n-pentylamine is used instead of ammonia and is reacted continuously with n-pentanol in the presence of sodium hydroxide to form tri-n-pentylamine. The molar ratio of n-pentylamine to n-pentanol is 1:4. The reaction temperature is 230-235° C., the total pressure is 60 bar, of which about 10 bar is made up by the hydrogen partial pressure. The molar ratio of tri-n-pentylamine to di-n-pentylamine in the output from the reaction was 1:0.1. Excess n-pentanol was not recirculated to the synthesis step.
According to claim 4, C1-C24-alcohols are used in pure form or in the form of their mixtures. Examples using methanol are not present in EP 257 443 A1.
According to EP 227 904 A1 (BASF AG), dimethylamine is reacted with ethanol or n-butanol in a similar way in the liquid phase to give dimethylethylamine or dimethyl-n-butylamine. The reaction is carried out in the presence of alkali metal hydroxide and a catalyst which comprises essentially only copper as active metal or is a pure copper catalyst. It is possible to use monohydric aliphatic alcohols having from 2 to 4 carbon atoms. Methanol is not mentioned in EP 227 904.
A disadvantage of the studies described in EP 257 443 A1 and EP 227 904 A1 is that the alkylation is preferably carried out in the presence of hydrogen. In all examples, the reaction is carried out in the presence of hydrogen. Specific safety measures have to be undertaken for this procedure. In addition, the alkali metal and/or alkaline earth metal oxides and alkali metal or alkaline earth metal hydroxides added to the reaction mixture have to be separated off again from the reaction product mixture after the alkylation reaction. In addition, when methanol is employed and is dehydrogenated to formaldehyde, the Cannizarro reaction can occur and in the presence of the basic alkali metal salts form methanol and alkali metal formate (Beyer/Walther, Lehrbuch der organischen Chemie, 24th edition, 2004, S. Hirzel-Verlag, page 215).
The fact that examples using methanol as alkylating agent are to be found neither in EP 257 443 nor in EP 227 904 may well be attributable to the potentially substantial by-product formation due to the Cannizarro reaction.
U.S. Pat. No. 4,910,304 A (BASF AG) discloses the preparation of N-methylpiperidine and N-methylmorpholine by reaction of pentanediol or diethylene glycol (DEG) with methylamine and 45% strength aqueous KOH solution over an all-active Cu/Al catalyst at 245° C. and 250 bar.
EP 137 478 A (BASF AG) relates to processes for preparing N-methylpiperidine or N-methylmorpholine by catalytic amination of pentanediol by means of methylamine in the gas phase at from 5 to 25 bar over a copper-comprising catalyst which has been obtained by heat treatment of a basic copper- and aluminum-comprising carbonate.
EP 235 651 A1 (BASF AG) teaches a process for preparing N-methylpiperazine from diethanolamine and methylamine over metal-comprising catalysts. The reaction is carried out in the liquid phase (downflow mode) (page 3, last paragraph). According to the example, a Cu/Al2O3 catalyst is used.
EP 816 350 A1 (BASF AG) describes processes for preparing N-methylpiperidine and N-methylmorpholine by reacting a primary amine with a diol in the liquid or gas phase over a copper catalyst which has been obtained by impregnation of SiO2 spheres with basic copper carbonate.
U.S. Pat. No. 4,739,051 A (BASF AG) teaches the preparation of morpholine and piperidine by reaction of DEG or pentanediol with ammonia under hydrogenating conditions in the gas phase at atmospheric pressure and 200° C. over an all-active Cu/Ni/Al catalyst.
EP 514 692 A2 (BASF AG) discloses processes for preparing amines from alcohols in the presence of catalysts comprising copper and nickel and zirconium oxide and/or aluminum oxide.
EP 440 829 A1 (U.S. Pat. No. 4,910,304) (BASF AG) describes the amination of diols over copper catalysts. The reaction is carried out in the liquid phase (downflow mode) (page 3, last paragraph). Suitable catalysts are the catalysts disclosed in DE 24 45 303 A (BASF AG), which can be obtained by heat treatment of a basic copper- and aluminum-comprising carbonate of the general composition CumAl6(CO3)0.5mO3(OH)m+12, where m is any, even nonintegral, number in the range from 2 to 6, for example the copper-comprising precipitated catalyst disclosed in loc. cit., example 1, which is prepared by treating a solution of copper nitrate and aluminum nitrate with sodium bicarbonate and subsequently washing, drying and heating the precipitate.
WO 07/036,496 A1 (BASF AG) describes the reaction of diethylene glycol with ammonia in the presence of Cu—Ni—Co catalysts.
WO 05/110969 A1 (BASF AG) describes a process for the continuous preparation of an amine by reaction of a primary or secondary alcohol, aldehyde and/or ketone with hydrogen and a nitrogen compound selected from the group consisting of ammonia, primary and secondary amines at a temperature in the range from 60 to 300° C. in the presence of a copper-comprising catalyst, where the catalytically active composition of the catalyst before reduction with hydrogen comprises from 20 to 85% by weight of aluminum oxide (Al2O3), zirconium dioxide (ZrO2), titanium dioxide (TiO2) and/or silicon dioxide (SiO2) and the reaction is carried out isothermally in the gas phase in a tube reactor.
WO 2010/031719 A1 (BASF SE) relates to a process for the continuous preparation of an amine by reaction of a primary or secondary alcohol, aldehyde and/or ketone with hydrogen and a nitrogen compound selected from the group consisting of ammonia, primary and secondary amines at a temperature in the range from 60 to 300° C. in the presence of a copper- and aluminum oxide-comprising catalyst, where the reaction is carried out in the gas phase and the catalytically active composition of the catalyst before reduction with hydrogen comprises aluminum oxide and oxygen-comprising compounds of copper and the shaped catalyst body is specified.